This application is the national phase of international application PCT/GB98/01715 filed Jun. 12, 1998 which designated the U.S.
This invention relates to a method for the manufacture of a finished product from a length of a lignocellulosic material.
It is well known to manufacture composite board products from wood derived feed stocks. Examples are medium density fibre board (MDF), high density fibre board, orientated strand board, chip board and the like. Such boards are most frequently bound by condensation resins such as the urea, melamine or resole phenol formaldehydes. A new trend is to use agricultural fibre as a feed stock, because excellent fibre is produced, the resource is rapidly regenerative, it removes the pressure on the timber resource. In this case the isocyanates are the desired binder because the nature of the surface and composition of agricultural fibres, the particle shape and specific surface area give rise to more critical binder requirements.
In the case of all lignocellulosic composite board products, plywoods, paper products and solid timber, particularly the softwoods and the marginal hardwoods, water is by far the greatest contributor to degradation.
There is therefore a requirement for the treatment of lignocellulosic products to make them highly water resistant.
This requirement may be achieved by the pre-treatment of lignocellulosic materials in particulate form as feed stock for board production, or veneers for plywood production, or by the post treatment of composite boards themselves, such as chip board or MDF, pump and paper products and solid timber. EP 0 107 155A, and DATABASE WPI Lepton Ch, Week 8530, AN 85-182725 both disclose methods for the production of lignocellulosic products with improved water resistance.
Subsidiary improvements such as improved mechanical properties, behavior in fire, absence of formaldehyde and resistance to microbial or insect attack may also be provided for.
There is always the need for improved methods of manufacture of products from lignocellulosic material.
According to the invention there is provided a method of improving the water resistance of a length of lignocellulosic material including the steps of:
(a) impregnating the length of lignocellulosic material through its depth with an impregnating composition comprising a solution of:
(i) a mineral oil;
(ii) a thermosetting resin and, if necessary, a catalyst therefor; and
(iii) a non-aqueous solvent for the mineral oil and for the thermosetting resin and catalyst therefor;
(b) removing the non-aqueous solvent from the product of step (a); and
(c) subjecting the product of step (b) to an elevated temperature to polymerise the thermosetting resin.
The term xe2x80x9ca length of a lignocellulosic materialxe2x80x9d includes lengths of solid wood, wood veneer and plywood; lengths of preformed composite boards such as chip board, medium density fibre board, high density fibre board, orientated strand board, and boards made from paper mill sludge, common mixed paper waste and sawdust; and lengths of virgin and recycled paper and cardboard.
The non-aqueous solvent is preferably dichloromethane or super critical liquid carbon dioxide.
The mineral oil and the thermosetting resin must be soluble in the non-aqueous solvent so that the impregnating composition is a solution
The thermosetting resin is preferably an isocyanate thermosetting resin or a precursor thereof, more preferably a resin derived from diphenylmethane-4,4xe2x80x2-diisocyanate (MDI).
The impregnating composition preferably comprises from 2% to 30% inclusive by mass of the impregnating composition of the mineral oil, preferably from 7% to 25% inclusive by mass of the impregnating composition of the mineral oil; from 1% to 25% inclusive by mass of the impregnating composition of the thermosetting resin optionally with a catalyst therefor, preferably from 2.5% to 15% inclusive by mass of the impregnating composition of the thermosetting resin optionally with a catalyst therefor; the remainder of the impregnating composition comprising the non-aqueous solvent and optional components, if any.
The impregnating composition is preferably impregnated into the length of the lignocellulosic material in an amount of from 0.4 to 2 parts inclusive by mass of the impregnating composition to 1 part by mass of the lignocellulosic material, preferably in the range of from 0.5 to 1.5 parts inclusive by mass of the impregnating composition to 1 part by mass of the lignocellulosic material. In general, the uptake depends upon the nature of the lignocellulosic material being treated.
In step (a), the impregnation may be carried out in any suitable manner, for example by immersion of the length of the lignocellulosic material in the impregnating composition, optionally with the application of pressure.
In step (b), the non-aqueous solvent may be removed in any suitable manner, for example by means of heat. The solvent, particularly when it is dichloromethane, is preferably recovered for reuse.
In step (c), the product of step (b) may be subjected to an elevated temperature in any suitable manner, for example in a heating chamber or kiln, to an elevated temperature which is sufficiently high to cause polymerisation of the thermosetting resin, for example a temperature of around 75xc2x0 C. to 185xc2x0 C. inclusive, preferably around 120xc2x0 C., for a sufficient period of time, for example from 0.5 to 3 hours inclusive, preferably around 1.5 hours. The impregnating composition may also include various optional components such as:
(iv) a preservative such as a bactericide, fungicide or insecticide, or the like preferably in an amount of from 0.25% to 5% inclusive by mass of the impregnating composition of the preservative;
(v) a dicarboxylic anhydride or a tricarboxylic anhydride soluble in the impregnating composition, preferably in an amount of from 0.5% to 8% inclusive by mass of the impregnating composition of the anhydride, preferably an amount of about 2.5% by mass of the impregnating composition of the anhydride;
(vi) other additives selected from fire retardants, ultraviolet light absorbers, dyes and anti-oxidants, and the like